"Boeing certified the 747-8 Intercontinental with the tail fuel tanks locked out because during design review of flight test data...it was discovered that, under a certain regulatory-required structural failure scenario, the airplane can experience flutter events when the fuel tanks in the horizontal stabiliser are filled over 15% of their capacity," said Boeing.

Reactivating the tanks and incorporating the fix will be be accomplished during normal maintenance operations as part of a service bulletin expected to be issued by the airframer once a solution is identified, said Boeing.

I wonder if this explains the recent reduction in predicted range despite the increase in payload. And are these tanks used to control the center of gravity, if so how to they compensate for not having that capability?

Quoting Daysleeper (Reply 3):
I wonder if this explains the recent reduction in predicted range despite the increase in payload. And are these tanks used to control the center of gravity, if so how to they compensate for not having that capability?

No, the reduction in stated range is due to higher payload at quoted range. Only the passenger version even has tail tanks.

The problem from what I've read is that is there is a flutter issue when there is a failure structural member . The FAA doesn't allow flutter in a single failure case.

I think they are saying that IF there is a certain structural failure then having over 15% load in the tail tank will cause flutter. As FAA rules state a single failure cannot cause flutter Boeing have decided to prevent any use of the tail tank until a solution is found. The tank can be reactivated during normal maintenance when instructed by Boeing.

Quoting QANTAS747-438 (Reply 5):Is Boeing saying that while the tail tank is there, they are never to use it?

No, it will be fixed:

Quoting art (Thread starter):Reactivating the tanks and incorporating the fix will be be accomplished during normal maintenance operations as part of a service bulletin expected to be issued by the airframer once a solution is identified, said Boeing.

LH said they still will get an 8,000 nm range from the B-747-8I in their 386 seat configueration. LH also said that is still a longer range than the A-380, in their configueration. Once the horizontial tail fuel tanks are activated, LH should get about an 8,400 nm range from their B-747-830Is.

"Boeing said the absence of tail fuel tanks will reduce the range of the VIP configured 747-8 by about 550-930km (300-400nm), depending on the aircraft's configuration."

"For our mission profile it's not a problem at the moment," said a Lufthansa spokesman, who said the tail fuel restriction would not restrict the aircraft's deployment on its initial routes, which have not yet been announced.

Boeing indicates the passenger capacity of the 747-8 as up to 467 seats in a three-class configuration. Lufthansa will operate the aircraft in a three-class configuration seating 386.

Lufthansa said it is "still quite positive that there will be a modification" that will restore access to the tail fuel tanks, but "of course you want an airplane that can run as long as possible" in unrestricted operation.

Lufthansa is "waiting to hear from Boeing how they will solve this problem," the airline added.

Despite not having a timeframe for a fix, the airline said it is its expectation that the restriction will not exist on deliveries in 2013."

"Lufthansa launched the 747-8 in December 2006 with an order for 20 of the General Electric GEnx-2B-powered aircraft. The 747-8 will have the longest range of any aircraft in the airline's fleet, it said, exceeding that of the Airbus A380.

The 747-8's range is advertised by Boeing as being around 14,800km (8,000nm) at maximum takeoff weight of 448t (987,000lb), though the airframer is currently updating the figure for its catalog specifications."

I might add LH also has 20 options in addition to the firm order for 20 B-747-830Is.

Quoting QANTAS747-438 (Reply 5):Is Boeing saying that while the tail tank is there, they are never to use it?

Quoting nighthawk (Reply 10):No, Boeing is saying currently they should not use it, until Boeing can come up with a fix for the flutter issue.

Boeing has stated airlines cannot use it until the fix is in place. The FAA is mandating they both pull the breaker in the cockpit that allows fuel to be transferred into the tank and to physically prevent fuel from being transferred by closing off the fittings.

Once Boeing has addressed the issue, then operators will be allowed to use the tank.

Quoting 777STL (Reply 13):I can't imagine it would be too much of an issue for them, it's not as if the aircraft is completely crippled in terms of range.

LH have stated they do not currently have any planned 747-8 route that would need them to use the auxiliary tanks. They do want the ability to have it for future needs, but for now, it won't affect their planned 747-8 operations.

Quoting KC135TopBoom (Reply 9):LH said they still will get an 8,000 nm range from the B-747-8I in their 386 seat configueration. LH also said that is still a longer range than the A-380, in their configueration.

In their configuration that is correct. In a different configuration the picture would be a little bit different, and slightly favoring the A380. .

But both 4-holers have a very good combination of passenger capacity, efficiency and range. No other aircraft on the market today offer these capabilities.

Quoting JAAlbert (Reply 16):In layperson's terms, what is a "failure structural member?" Can you give some examples so the technologically challenged among us (me) can visualize this?

Essentially, the horizontal stabilizer is fine with fuel in it (during normal flight envelopes/loads).

However, if there is a failure in the wing-to-strut join fitting, if the tailplane tank is filled beyond 15%, this creates a flutter situation. FAA regulations do not allow such a scenario, so Boeing cannot currently allow the aft tank to be filled beyond 15%.

Boeing have stated that such a failure has never happened in the operational history of the 747, but the FAA will not grant them a waiver and Boeing must deactivate the system until they have developed and installed a fix.

Check out the video at the 1:14 mark in particular. You don't want your 747 to look like that in flight. Obviously the flutter situation on the 747-8I's tailplanes would not be that extreme, but the video gives a good illustration of the concept (as well as some great wind tunnel disaster footage!).